The Inbetweeners 2 can be almost unbelievably crass – one character urinates in another’s face and there is a water slide chase sequence involving faeces. This is, of course, the kind of thing that has proved popular in comedy since before Aristophanes married political satire to gags about engorged phalluses and hurling shit at the faces of subpar poets.

The success of The Inbetweeners can partly be explained by its ability to go beyond crassness. As in South Park, the cleverer stuff is smuggled in under a cloak of gross-out humour. It has become a hit without a scorched-earth marketing campaign, the shock and awe of special effects or even the good looks of its stars. For this we should be thankful. So much of what we think of as being popular has actually just been boosted to prominence, remorselessly shovelled at us until we give in and open our mouths. Nobody really watched the first series of The Inbetweeners until it moved from E4 to Channel 4. When it was broadcast again, it took off. All it needed was a chance to be seen, so its success felt organic.

But there’s something else beyond comedy going on that is relatively radical for mass-appeal cinema: the protagonists, both in the series and in the movies, appear to be quite “normal”. The four are hapless teenagers a focus group of the nation could identify with. They are “in-between” the cool kids and the lame kids, they don’t belong to any potentially alienating subculture and they are from the suburbs not the estates (neither inner-city ones nor the private, country kind).

These lads are all white, privileged males – but they are white privileged males not normally shown on the big screen.

They aren’t cool and they aren’t slick. They’ll get invited to the party because they are nice guys but they won’t take drugs and have sex; they’ll turn up dressed as Harry Potter and have to leave. The subversion of this blandness comes with the characters themselves. They remind us of the oddity of normality.

Caught between childhood and adulthood, between social acceptance and social exclusion, the four leads are the perfect conduits for gags about the pain of growing up, fitting in and dealing with the world. And British audiences, scared or put off as they can be by difference, have never been scared by these characters. They can look up at the big screen and see themselves.

The physical comedy – a peculiarly British take on the American high school film, such as American Pie and Superbad – provides a vicarious, nostalgic thrill for people whose adolescences never really got wild and crazy. In a world in which adolescence has been stretched out, the appeal of a bunch of teenagers (played, of course, by adults) struggling with these things in a comic way is that much stronger.

Jokes are made about absent parents. Families are shown to be a source of pain and embarrassment. The mortifying, drawn-out process of growing up is treated sensitively. There are no fairytale endings – one character goes into the Australian outback to win back his ex-girlfriend. She tells him warmly that she’s not interested.

Life is lived in a continuing state of emergency but friendship prevails. The desperation of the main characters turns them into a team the British filmgoing public can support. They come to support the “normal” guys, but they are then shown that there isn’t really any such thing as normal.